Copyright (c) 1994 J. Adams, W. Brainerd, J. Martin, and B. Smith.
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This file may not be copied without permission of the authors.

22 Defined Type: Structure Component

A structure component is a component of an object of user-defined type. Where the name of the component is accessible, the component may be referenced and used like any other variable. The reference may appear in an expression or as the variable on the lefthand side of an assignment statement. In the latter case, a vlaue is assigned to the component. The name of the component is accessible in a scoping unit that contains the type definition, whose host contains the type defrinition, or where the type definition is publicly accessible by use association. A component may be a scalar, an explicit-shape array, or, if it has the POINTER attribute, a deferred-shape array.

Examples:

TYPE REG_FORM          ! REG_FORM is a defined type.
   CHARACTER (30) LAST_NAME, FIRST_NAME
   INTEGER ID_NUM      ! Note that ID_NUM in REG_FORM does not
   CHARACTER (2) GRADE !  conflict with ID_NUM in CLASS because
END TYPE REG_FORM      !  each type definition is a scoping unit.

TYPE CLASS                       ! CLASS is a simple defined type
   INTEGER YEAR, QUARTER, ID_NUM !  that includes another
   CHARACTER(30) INSTRUCTOR      !  defined type as a component.
   TYPE (REG_FORM) STUDENT(40)
END TYPE CLASS

TYPE (CLASS) ALGEBRA, CHEMISTRY  ! Two structures of type CLASS
TYPE (REG_FORM) TRANSFERS(20)    ! An array of structures

ALGEBRA % INSTRUCTOR = "Brown"             ! Some typical uses
ALGEBRA % ID_NUM = 101                     !   of structure
ALGEBRA % STUDENT(1) % ID_NUM = 593010040  !   components
CHEMISTRY % STUDENT(39) % LAST_NAME = "Flake"
CHEMISTRY % STUDENT(39) % GRADE = "F-"
   . . .
ALGEBRA % STUDENT(27:33) = TRANSFERS(1:7)  ! An array assignment
ALGEBRA % STUDENT(6:8) % GRADE = "B+"      ! The B+ is broadcast.
PRINT *, CHEMISTRY % STUDENT(1:33)         ! Print 33 students.

Related Topics:

Character Substrings
Defined Type: Definition
Defined Type: Objects
Variables

To Read More About It:

ISO 1539 : 1991, Fortran Standard, 6.1.2
Fortran 90 Handbook, 6.3
Programmer's Guide to Fortran 90, 6.3.1

A structure component reference is:

part-reference [ % part-reference ]...

A part reference is:

part-name [ ( section-subscript-list ) ]

A section subscript is one of:

subscript
subscript-triplet
vector-subscript

A subscript triplet is:

[ subscript ] : [ subscript ] [ : subscript ]

A vector subscript is:

rank-one-integer-array

A substring of a structure component is:

part-reference [ % part-name ]... ( starting-position : ending-position )

Things To Know:

1. In a structure component reference, each part name except the rightmost one must be of defined type, each part name except the leftmost one must be the name of a component of the preceding defined type, and the leftmost part name is the name of a structured object.
2. The type and type parameters of a structure component are those of the rightmost part name. A structure component is a pointer only if the rightmost part name has the POINTER attribute.
3. If the leftmost part name has the INTENT, TARGET, or PARAMETER attribute, the structure component has that attribute.
4. In a structure component reference, only one part may be array valued, in which case the reference is an array reference. This is an arbitrary restriction in the language, imposed for simplicity.
5. If a structure component reference is an array reference, no part to the right of the array part may have the POINTER attribute. It is possible to declare an array of structures that have a pointer component, but it is not possible to have an array-valued reference to such an object. The reason for this is that Fortran 90 allows pointers to arrays, but does not provide for arrays of pointers.
6. If the type definition is in a module and contains an internal PRIVATE statement, the internal structure, including the number, names, and types of the components are not accessible outside the module. If the type itself is public, objects of this type may be declared and used outside